My invention is an improvement in four-wheel-drive powertrains having an internal combustion engine and a multiple-ratio, geared transmission. The crankshaft of the engine is connected to torque input gearing of the transmission and the output shaft of the transmission is connected to a rear drive shaft, which delivers torque to a rear differential and to rear traction wheels for the vehicle.
A transfer case normally is used to provide a torque flow path to the front vehicle wheels of an all-wheel drive vehicle. The transfer case in a typical arrangement would be assembled on the housing of the multiple-ratio transmission. A drive chain may be used to connect drivably a torque output element of the transmission to a torque input element of the transfer gear case. The power input shaft of the transfer gear case, in a typical environment, would be connected to a sun gear of a planetary gear unit. The ring gear of the planetary gear unit would be fixed. A carrier for such planetary gear units carries a pinion assembly comprising pinions drivably engaged with the sun gear and the ring gear. The carrier is the torque output element of the transfer case planetary gearing.
A positive engagement clutch may be used to connect drivably the rear output shaft of the transfer case to the power input shaft for the transfer case, the latter being connected to the output of the multiple-ratio transmission. When the positive engagement clutch is shifted in the opposite direction, the power input sun gear drives the rear output shaft for the transfer case through the planetary gearing as the carrier becomes connected to the rear output shaft. When the positive engagement clutch is moved to an intermediate position, the torque delivery path from the power input shaft for the transfer case is interrupted and a connection between the rear output shaft and the carrier is disestablished.
Thus, the transfer case has three operating modes; i.e., a four-wheel, high-speed mode, a four-wheel, low-speed mode and a neutral mode. A secondary clutch assembly is used to disconnect the drive chain from the rear output shaft if it is desired to operate the vehicle in a two-wheel-drive mode.